1. Field of the Invention
The disclosures herein generally relate to a semiconductor device, a manufacturing method thereof and an imaging apparatus.
2. Description of the Related Art
A phototransistor having a bipolar structure has a feature of amplifying an electric current according to a physical property, which the bipolar structure has, on outputting a photo-electric current obtained at a photo diode located between a collector and a base from an emitter. Therefore, sensitivity is enhanced with a smaller light-receiving area in a case where light intensity is low.
However, although the sensitivity in the case where light intensity is low is enhanced, the photo transistor has a difficult aspect in a treatment, such that careful handling is required for saturation of an output signal, since the photo-electric current increases, as the light intensity becomes greater. Then, for example, Japanese Published Patent Application No. 2013-187527 discloses a technique of varying sensitivity for light intensity by varying a current amplification factor of a photo transistor, and thereby obtaining a proper sensitivity for each of the light intensities.